| Due to the excellent properties of polyethylene materials,the amount of use in life is increasing,and it is widely used in gas pipelines.However,in the manufacturing process of polyethylene gas pipe,the thickness control and whether there is a certain defect is an important factor for the quality of pipeline production.However,the commonly used detection method is mainly ultrasonic,and the detection method is susceptible to environmental temperature and humidity Therefore,this paper proposes a method based on pulsed terahertz time-domain spectroscopy detection,and conducts a series of systematic studies on the optical parameters,thickness detection and defect detection of polyethylene materials.The main contents are as follows:First,using terahertz time-domain spectroscopy system,the birefringence of different polyethylene samples was measured by transmission method,and the change of refractive index under different frequencies was studied.The results show that the refractive indices of different samples are different,and the refractive indices of the samples vary with different frequencies.The average refractive index of PE80 sample is slightly lower than that of PE100 sample.The refractive index of the sample in the same sample first increases,enters the stable state and finally decreases gradually.The average refractive index of PE80 shows a steady trend in 0.2~1.2THz,which is called the effective area.The refractive index is about 1.9677;PE100 is about 1.9273.Second,the terahertz time-domain spectroscopy was used to measure the peak time difference of the time-domain waveform at a certain point in the sample.A single-point thickness measurement model was established to measure the thickness of polyethylene test blocks with different thickness from 5 to 15 mm.The error was analyzed.The results show that the relative error of the measurement method is less than 2%.The main sources of error are the reference sample thickness error and system error.In the meantime,a new measurement method is proposed based on theabove principle of thickness measurement.In addition,the measurement platform is built,which not only does not need to know the refractive index information of the tested sample,but also realizes the simultaneous measurement of the refractive index and the thickness of the tested sample Measurement,improve the detection accuracy.Third,the imaging method based on pulsed terahertz time-domain spectroscopy was studied first,and the method of maximum value calculation was used to design a standard polyethylene with a size of 25 × 100× 100 mm with different defects of0.2~2mm and depth of 1~15mm Block test imaging test.From the imaging point of view to strengthen the quality control of polyethylene pipe to make it a better guarantee. |
